特提斯喜马拉雅铅锌锑金成矿带含炭质岩石中热液脉型矿床的综合电法勘探——以西藏扎西康铅锌锑多金属矿为例

扎西康铅锌锑多金属矿床产出于特提斯喜马拉雅炭质板岩的断裂带内,是特提斯喜马拉雅铅锌锑金成矿带内典型的热液脉型矿床。由于含炭质岩石和金属硫化物都呈现出相似的低阻高极化电性特征,加之热液脉型矿床的矿体普遍较小,使得在含炭质岩石中对金属硫化物矿体进行电法勘探存在较大困难。本文通过对扎西康矿床已知矿体的音频大地电磁测深和激电中梯测量,发现矿区的炭质板岩呈现低电阻率(10^-0.4~10⁰Ω·m)和高极化率(9%~20%)特征,而矿体呈现出高电阻率(10²~10³Ω·m)和低极化率(1%~5%)的特征。经研究分析,认为造成这种现象的原因有两方面：(1)扎西康炭质板岩中的炭质物质量分数平均为0.79%,变质温度约在300±25℃~340±25℃,炭质物电阻率为6.1×10^-5~6.8×10^-4Ω·m,显示极好的导电性;此外,炭质板岩中存在大量黏土矿物,黏土矿物的吸水性促进了炭质物的连通性,因此炭质物高导电性与连通性的耦合使得炭质板岩呈现低阻高极化电性特征;(2)扎西康矿床的脉型矿体除包含金属硫化物外,还产出大量的脉石矿物,脉石矿物普遍具有高阻低极化电性特征,是造成整个矿体在炭质板岩中呈现高阻低极化异常的根本原因。据此,本文提出在炭质板岩中通过识别脉石矿物引起的高阻低极化异常带间接找矿的新思路,相应的技术方法组合为：利用激电中梯测量定位高阻低极化带的平面位置,再利用音频大地电磁测深探测其深部产状。     

藏南扎西康铅锌锑银多金属矿床地质特征及找矿方向

扎西康铅锌锑银矿区主要出露下侏罗统地层。矿区内目前发现的4个铅锌锑银矿体,主要充填于近南北向张扭性断裂破碎带及次级羽状张节理中,矿化强度从构造带中心向两侧围岩呈渐变过渡关系。初步分析矿床与北部的穷多江变质核杂岩、广泛发育的南北向断裂及侏罗纪地层有着密切成因联系。F42、F46、F48所围限的倒三角形区域内的侏罗纪地层、南北向深大断裂和褶皱核部区域,应为今后矿区及外围进一步探矿的重点和主要研究对象。     

应用能谱扫描电镜与X射线衍射等分析技术研究西藏扎西康铅锌矿中伴生元素锰的赋存状态

西藏扎西康铅锌多金属矿床是我国首次发现的喷流沉积-热泉水改造型锰铁锑铅锌银矿床,已有研究表明矿床中除了铅锌矿还伴生有银、锑、铜、硫、锰、砷等多种元素。本文在化学多元素分析和光学显微镜镜下鉴定的基础上,结合能谱扫描电子显微镜和X射线衍射分析等手段对扎西康铅锌矿中伴生组分Mn的含量、矿物种类、嵌布和包裹等特性进行了研究。分析结果表明,原生矿石的主要成矿元素Pb和Zn的含量分别为6.00%和4.00%,伴生元素Mn的含量平均达到4.36%;原生矿石中的主要矿物为方铅矿、闪锌矿,其次为黄铁矿、毒砂和菱锰矿等。原生矿石中伴生元素Mn主要以独立的菱锰矿和铁菱锰矿形式存在,与闪锌矿和方铅矿密切共生,是成矿早期重要的载矿矿物,嵌布在石英、黄铁矿、闪锌矿和毒砂的粒间、边部及空隙间,其次以类质同象形式赋存于菱铁矿和菱锌矿中。进一步对扎西康铅锌矿选冶产物中的伴生元素Mn的含量和赋存状态进行研究,研究表明Mn具有较高的综合利用价值,在原生矿石、铅精矿、锌精矿和尾矿中的质量分数分别为4.36%、0.51%、0.95%和5.36%,显示Mn很少一部分进入铅精矿和锌精矿,而绝大部分进入尾矿;Mn在尾矿中仍主要以菱锰矿形式存在,存在形式与原生矿石相比未发生改变,可通过强磁选工艺从铅锌尾矿中综合回收利用Mn。     

西藏扎西康多金属矿床成矿过程中的流体性质演化初探

扎西康铅锌银锑多金属矿床是北喜马拉雅成矿带中重要的铅锌锑多金属矿床,对其成矿过程的研究对其深部资源预测具有重要的指导意义。本文通过野外地质调查结合成矿流体包裹体研究,获得该矿床成矿前硅化、成矿早期铁锰碳酸盐化、中早期毒砂黄铁矿化、中期含铅锌硅化、晚期含锑硅化和成矿后硅化方解石化的流体温度分别为297、280、264、251、215~247和183~237℃,盐度分别为17.80%、8.39%、6.50%、5.98%、2.75%-5.29%和4.28%Na Cleq(wt)。研究表明,成矿流体为顺断裂运移的具有显著岩浆贡献的中高温、中等盐度、较高硫逸度含CO2、CH4和N2的热液与中温低盐度下渗大气降水在断裂中混合的产物。两者的混合改变了流体温度、盐度和硫逸度等进而沉淀金属矿物形成矿体。锑矿化温度低于铅锌矿化温度,下部~247℃锑矿化的发现暗示深部有进一步找矿的空间。     

西藏扎西康锌多金属矿床地质特征及银的赋存状态研究

扎西康锌多金属矿床位于西藏特提斯喜马拉雅板片的"金锑多金属"成矿带东段。研究显示,矿体主要呈脉状、透镜状产于近南北向的张性断裂中。热液成矿作用主要可划分为早、晚2个成矿阶段,7个成矿亚阶段,早期以铅锌矿化为主,晚期以锑(铅)矿化为主。岩矿石镜下鉴定和电子探针分析表明,扎西康矿床矿石种类繁多,矿物组合和成矿元素均呈现明显的分带现象,由深至浅(W→E)为含锡(铁)闪锌矿+铁锰碳酸盐+少量方铅矿+少量黄铜矿(深部)→(铁)闪锌矿+铁锰碳酸盐+少量方铅矿+黄铁矿+毒砂+少量银黝铜矿+少量石英(中深部)→方铅矿+闪锌矿+脆硫锑铅矿+铁锰碳酸盐+硫锑铅矿+少量银黝铜矿+石英(中部)→辉锑矿+方铅矿+少量闪锌矿+石英+少量铁锰碳酸盐(浅部),对应的元素分带为Zn(Pb+Ag+Cu+Sn)→Zn(Pb+Ag)→Zn+Pb(Sb+Ag)→Pb+Sb+Ag+Zn。矿区银矿化主要集中在Ⅴ号矿体ZK2703-ZK2302、ZK1502-ZK1105和ZK806三个区域,与铅锑矿化关系密切。矿石中银主要以类质同象的形式存在,独立银矿物相对较少。其中,类质同象银主要赋存在方铅矿中,少量赋存在硫锑铅矿、脆硫锑铅矿、毒砂、黄铁矿等金属硫化物中;独立银矿物有少量的银黝铜矿、硫锑铅银矿、银(含银)硫铜锑矿。成矿流体中铅、锌、锑、银的运移和富集沉淀是受体系中温度、压力、浓度、pH值等多种因素综合控制的结果。     

Characteristics of Pegmatite-Related Fluids and Significance to Ore-Forming Processes in the Zhaxikang Pb-Zn-Sb Polymetallic Deposit, Tibet, China

The Zhaxikang Pb-Zn-Sb polymetallic deposit is one of the most important deposits in the newly recognized southern Tibet antimony-gold metallogenic belt.Compared to the porphyry deposits in the Gangdese belt,much less researches have addressed these deposits,and the genesis of the Zhaxikang deposit is still controversial.Based on field investigation,petrographic,microthermometric,Laser Raman Microprobe（LRM） and SEM/EDS analyses of fluid,melt-fluid,melt and solid inclusions in quartz and beryl from pegmatite,this paper documents the characteristics and the evolution of primary magmatic fluid which was genetically related to greisenization,pegmatitization,and silification in the area.The results show that the primary magmatic fluids were derived from unmixing between melt and fluid and underwent a phase separation process soon after the exsolution.The primary magmatic fluids are of low salinity,high temperature,and can be approximated by the H₂O-NaCl-CO₂ system.The presence of Mn-Fe carbonate in melt-fluid inclusions and a Zn-bearing mineral（gahnite） trapped in beryl and in inclusions from pegmatite indicates high Mn,Fe,and Zn concentrations in the parent magma and magmatic fluids,and implies a genetic link between pegmatite and Pb-Zn-Sb mineralization.High B and F concentrations in the parent magma largely lower the solidus of the magma and lead to late fluid exsolution,thus the primary magmatic fluids related to pegmatite have much lower temperature than those in most porphyry systems.Boiling of the primary magmatic fluids leads to high-salinity and high-temperature fluids which have high capacity to transport Pb,Zn and Sb.The decrease in temperature and mixing with fluids from other sources may have caused the precipitation of Pb-Zn-Sn（Au） minerals in the distal fault systems surrounding the causative intrusion.     

西藏扎西康铅锌锑多金属矿地质特征及矿床成因探讨

扎西康铅锌锑多金属矿已发现规模较大的四个矿体,控制资源量达100万吨以上.矿体均分布在NNW或NNE张扭性断裂破碎带内,受断裂破碎带控制,矿体与围岩界线明显.铅同位素位组成显示成矿物质主要来源于上地壳,包裹体研究成矿流体为中低温-低盐度成矿,氢、氧、硅同位素组成显示成矿流体主要为大气降水下渗循环构成的地热水.硫同位素特...     

天然源面波法在西藏扎西康矿区采空区勘察中的应用

天然源面波勘探是从自然界的各种微小振动中提取出瑞雷面波,经过面波频散曲线的反演得到岩层速度结构,达到推测地下岩层和构造分布状况的目的。该方法克服了人工源激发困难的问题,对场地适应性强,有效探测深度较大,探测结果具有分辨率高、抗干扰能力强等特点。文章以扎西康矿区采空区勘察中的应用为例,介绍了天然源面波法特点、优势及应用效果。     

The Zhaxikang Vein‐type Pb‐Zn‐Ag‐Sb Deposit in Himalayan Orogen,Tibet: Product by Overprinting and Remobilization Processes during Post‐collisional Period

The Zhaxikang Pb-Zn-Ag-Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein-type mineralization that hosts multiple mineral assemblages and complicated metal associations. The deposit consists of at least six steeply dipping veintype orebodies that are hosted by Early Jurassic black carbonaceous slates and are controlled by a Cenozoic N–S-striking normal fault system. This deposit records multiple stages of mineralization that include an early period(A) of massive coarse-grained galena–sphalerite deposition and a later period(B) of Sb-bearing vein-type mineralization. Period A is only associated with galena–sphalerite mineralization, whereas period B can be subdivided into ferrous rhodochrosite–sphalerite–pyrite, quartz–sulfosalt–sphalerite, calcite–pyrite, quartz–stibnite, and quartz-only stages of mineralization. The formation of brecciated galena and sphalerite ores during period A implies reworking of pre-existing Pb–Zn sulfides by Cenozoic tectonic deformation, whereas period B mineralization records extensive openspace filling during ore formation. Fluid inclusion microthermometric data indicate that both periods A and B were associated with low–medium temperature(187–267°C) and low salinity(4.00–10.18% wt. Na Cl equivalent) ore-forming fluids, although variations in the physical–chemical nature of the period B fluids suggest that this phase of mineralization was characterized by variable water/rock ratios. Microprobe analyses indicate that Fe concentrations in sphalerite decrease from period A to period B, and can be divided into three groups with Fe S concentrations of 8.999–9.577, 7.125–9.109, 5.438–1.460 mol.%. The concentrations of Zn, Sb, Pb, and Ag within orebodies in the study area are normally distributed in both lateral and vertical directions, and Pb, Sb, and/or Ag concentrations are positive correlation within the central part of these orebodies, but negatively correlate in the margins. Sulfide S isotope compositions are highly variable(4‰–13‰), varying from 4‰ to 11‰ in period A and 10‰ to 13‰ in period B. The Pb isotope within these samples is highly radiogenic and defines linear trends in 206 Pb/204 Pb vs. 207 Pb/204 Pb and 206 Pb/204 Pb vs. 208 Pb/204 Pb diagrams, respectively. The S and Pb isotopic characteristics indicate that the period B orebodies formed by mixing of Pb–Zn sulfides and regional Sbbearing fluids. These features are indicative of overprinting and remobilization of pre-existing Pb–Zn sulfides by Sb-bearing ore-forming fluids during a post-collisional period of the Himalayan Orogeny. The presence of similar ore types in the north Rhenish Massif that formed after the Variscan Orogeny suggests that Zhaxikang-style mineralization may be present in other orogenic belts, suggesting that this deposit may guide Pb–Zn exploration in these areas.     

藏南扎西康矿区流纹岩的岩石地球化学、 锆石U Pb测年和Hf同位素组成

本文对藏南扎西康铅锌锑银矿区流纹岩进行详细的岩石地球化学、锆石U Pb年代学和Hf同位素组成研究。详细的地球化学特征显示,扎西康流纹岩具有富硅（SiO2=73.37%~77.08%）、贫碱（Na2O+K2O=3.48%~3.56%）,贫Mg（MgO=0.36%~0.49%）,贫Ca（CaO=0.50%~0.66%）,强过铝质（A/CNK=2.16~2.62）, 富集Rb、Th、U、Pb等大离子亲石元素及Hf、Nd等高场强元素,并明显亏损Sr、Ti等元素。稀土总量较高（∑REE=295.71×10-6~343.82×10-6）,轻稀土富集,且轻重稀土分异明显（LREE/HREE=10.00~12.62）,弱负Eu异常（δEu=0.57~0.88）,无明显Ce异常。采用LA MC ICP MS对流纹岩锆石U Pb年龄进行测定,岩体成岩年龄为135.33±0.62Ma。锆石εHf(t)值较低,主要集中在-9.5~-24.2,显示其物源为壳源。扎西康矿区出露的流纹岩形成于早白垩世,可能是Comei—Bunury大火成岩省的一部分。